membershipworks: Use django.utils.timezone.now instead of django.db.models.functions.Now

`Now()` produces incorrect results due to timezone mismatch, see
https://code.djangoproject.com/ticket/31638

membershipworks/tasks/event_survey_emails.py

@@ -4,7 +4,7 @@ from urllib.parse import quote, urlencode
 
 from django.conf import settings
 from django.core import mail
-from django.db.models.functions import Now
+from django.utils import timezone
 
 from cmsmanage.django_q2_helper import q_task_group
 from cmsmanage.email import TemplatedMultipartEmail
@@ -62,8 +62,14 @@ class EventSurveyEmail(TemplatedMultipartEmail):
 @q_task_group("Send Event Survey Emails")
 def send_survey_emails():
     with mail.get_connection() as conn:
+        # not using django.db.models.functions.Now() because of
+        # timezone mismatch, see
+        # https://code.djangoproject.com/ticket/31638
         for event in EventExt.objects.filter(
-            occurred=True, should_survey=True, survey_email_sent=False, end__lt=Now()
+            occurred=True,
+            should_survey=True,
+            survey_email_sent=False,
+            end__lt=timezone.now(),
         ):
             logger.info("Sending survey messages for event: %s", event)